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 Reduction of E-R diagrams

Let there be ‘m’ number of entities and ‘n’ number of relationships in a given E-R diagram.

The number of relations, after converting the E-R diagram to relations, is m+n.

 

Example 1:

Image Source

 

In the above example, m = 2 and n = 1. (Two entities and one relationship)

The attributes in the relationship table are the combination of primary keys of the entities that are connected through this relationship.

Table-1 :  INSTRUCTOR : ID, I-name, salary

Table-2 : STUDENT : ID, S-name, tot_credits

Table-3 : ADVISOR : I-ID, S-ID

 

Example 2:

Image Reference

In the above example, the tables are :

Table-1 : INSTRUCTOR : I-ID, I-name, salary

Table-2 : STUDENT : S-ID, I-name, tot_cred

Table-3 : PROJECT  : P-ID, P-Name

Table-4 : PROJ-GUIDE : I-ID, S-ID, P-ID

Reference :

Reduction of E-R Diagrams.